A high-profile campaign by the Optimum Population Trust, supported by such luminaries as government advisor Jonathon Porritt and broadcaster David Attenborough, seeks to encourage couples worldwide to limit their families to two children. The ‘Stop At Two’ campaign is premised on the idea that unrestrained population growth will damage the environment. But some argue that fears about the environmental effects of population growth represent a new form of Malthusianism, the old idea that population growth will push society up against natural limits.

Critics of the ‘Stop At Two’ campaign point out that Malthusianism was discredited by historical developments, and suggest the same will be true of today’s fears. They argue that we can tackle environmental problems without limiting the world population, and that ‘reproductive choice’ should mean people make decisions about having children based on their own desires and circumstances. Some worry that Western NGOs campaigning for contraception and sex education in the developing world under the banner of women’s rights are in fact promoting a Malthusian agenda, pointing to the repressive history of state population control programmes. But sympathisers with the ‘Stop At Two’ campaign stress this is about individuals making choices; and what is wrong with encouraging them to take the environment into account?

Where does ‘family planning’ stop being about individuals and couples making their own reproductive decisions and become a moral imperative that people should make the ‘right choices’? Are fears about population growth a new form of an old panic, or is the expanding carbon footprint a problem we need to address by limiting population growth? What circumstances and concerns do people take into account when they plan their families today?

Family planning is supposed to be something that women, and their partners, do in order to shape their childbearing choices around their lives. The way the concept is promoted today often implies that the planning should be done for us, or despite us, according to an abstract set of rules; and that we adults should be shaping our childbearing choices around the babies we do not yet have.

The report, Fewer Emitters, Lower Emissions, Less Cost, commissioned by the Optimum Population Trust from the London School of Economics, concludes that “considered purely as a method of reducing future CO2 emissions”, family planning is more cost-effective than leading low-carbon technologies. It says family planning should be seen as one of the primary methods of emissions reduction.

The annual Social Trends study published earlier this week by the Office for National Statistics states that the number of people in the UK is growing by 1,000 a day. There are 61 million people officially resident in Britain today and this is expected to grow by 4.4 million by 2016.

The more children we have, the more stress we put on an already overburdened planet, say campaigners. Observer environment correspondent Juliette Jowit meets the modern Malthusians who, for the sake of the planet, are choosing to 'stop at two'

Since the beginning of time, one of the clearest markers of an enlightened society has been the moral status it attaches to human life. And outwardly, at least, twenty-first-century Western societies express an unprecedented degree of respect for human life.